Transmitting apparatus for railway train communication systems



Aug 17, 1943. A. M. CRAVATH' 2,327,249

TRANSMITTING APPARATUS FOR RAILWAY TRAIN COMMUNICATION SYSTEMS Filed June 25, 1942 M 2 PFf P32 5 7 Patented Aug. 17, 1943 TRANSMITTING APPARATUS FOR RAILWAY YTRAIN COMMUNICATION SYSTEMS Austin Cravath, San Francisco, Calif., assignor to The Union Switch and Signal Company, Swissvale, Pa., a corporation of Pennsyl- Y Vania v Application June 25, 1942, Serial No. 448,33)

i. i Claims.

My invention relates to transmitting apparatus for railway train communication systems, and` more particularly to transmitting apparatus for railway train communication systems which use the track railsas conductors of a transmitting circuit.

In a railway train communication system which l usesthe track rails in the transmitting circuit,

the transmitting apparatuson 'a train is frequently conductively coupled to Vthe"transrnitting circuit by a sending loop circuit which isr inter-v posed between the transmitting apparatus and two pairs of wheels of thetrain,V such sending loop circuit including thev wheel-to-rail contact andthe length of rail between the two pairs'of wheels. The current flowing in this sending loop circuitcreates a voltage drop across such length of rail, and such voltagel drop iti-turn causesl communication current to flow in'therails in multiple and thro-ugh the rail-to-ground impedance. In order to createa relatively large vol*- age drop across such rail length, the sending loop circuit is tuned/for the communication current and is proportioned for an impedance that places a full load on the transmitting apparatus. When a train stops or isy moving at a very low'speed, there may be avery highresi'stance, amounting to practically an open circuit, forsuch sending loop circuit due to the rust and dirt between' the wheels and the rails. That is to say, a high resista-nce wheel-to-rail Contact may occur due to the surface condition of the rails. Y A feature of my invention is the provision of train carried transmitting apparatus of the type hererinvolved incorporating novel and improved means wherewith a relatively high temporary voltage is created to break down the resistance of a wheel-.to-rail contact. f

Still another feature of my invention is the provision of train carried transmitting apparatus incorporating novelmeans for conditioning an associated sending loop circuit sowas to place the full normal output load on the transmitting apparatus independent of the usual Vpath through the wheel-to--rail contacts and rails and to create a relatively high temporary Voltage across the,

circuit conductors connected to the wheels.

Again, a feature of my invention is the 'provision of train carried transmitting apparatus incorporating an improved series-parallel tuned sending loopcircuit for conductively coupling* invention will appear -asVV the specification progresses. 1 y

The above features and advantages embodying my invention I attain by providing 4a low power factor inductance, a special load reactance and a special switching means. 'I'he switching means is operable to connect the low power factor inductance across the loop circuit conductors leads ing to the wheels at which contacts are made to the rails, and to connectAthe/specialload reactl ance to the transmitting apparatus. In this way a temporary circuit is formed by the special reactance and inductance and which circuit causes substantially the full load current to be supplied by the transmitting apparatus anda'resultant relatively high' voltage developed across the' low powerfaotor inductance. The inductance beingV connected across the conductors leading tothe wheels, this high voltage is applied across the wheel-to-rail contact to break 'clown the resistance of the wheel-to-rail contact. Ordinarily the breaking down of the resistance of the wheelto-rail contact is effected almost immediately and hence a short period set up by the switching means is all that is required. The sending loop circuit may be series tuned or parall'eltuned as has been used heretofore, but'I have found that a series-parallel Vtuned circuit has special advantages.

I shall describe three forms of apparatus embodying my invention, and shall-then point out the novel features thereof in claims. l

In the accompanying drawing,`Fig. 1 is a dia-V grammatic view showing one` form of apparatusv embodying my invention when used with train carried transmitting apparatus using a `series tuned sending loop circuit. Fig. 2 is a diagrammaticview sho-wing another form of apparatus embodying my invention when used withtrain' carried transmitting apparatus using a parallel tuned sending loop circuit. Fig.`3 is a diagrammatic View showing train carriedjtransmitting apparatus provided with aV series-parallel tuned sendingloop circuit andl which 'apparatus also embodies'my invention. In each of. the different views like reference characters areV used to designate similar parts. i

Referring to Fig. 1, the reference character CO designates a'vehicle of airailway'train, such as, for example, a Caboose of afreight train. This vehicle CO has mounted thereonfcomrnunication apparatus which ordinarily comprises transmitting apparatus and receiving apparatus. As here shown, the transmitting apparatus includes `as essential elements a modulator MO, an oscillator 2iv s '2,327,249

tion of each forms no part of my present inven-N tion. For example, these elements of the trans? mitting apparatus may be similar to those ,disv,

closed by Letters Patent ci the United4 States lilo,V

2,064,639, granted December' l5, i936lto Leland D.

Whitelocl; et al. for Communication syst'enisflt, is sufficient for Ythe present application to .pointw i out that voice frequencies produced in 'a' microphone M and the carrier frequency current generated at oscillator OS are mixed at modulator MO to produce upper and lower side bands ot., Band pass filter BPF is proportioned the carrier. to pass apreselected one of the side bands to the power amplifier PA where such side band clllfentl isY ampliiied in the plate circuits ottwo electron tubes 4 and 5. The plate circuits, for tubes 4 and. 5' include windings and 'l, .::espectively, of, output transformer T l bereierredgto later.r A condenser CB'is prefer.-

ably vconnected across the Winding of relayRF.,

The Vcommunicationapparatus mounted on ca boose CO would ordinarily include receiving ape paratus so as to provide two way communication,y but such receiving apparatus. isomitted from. th e drawing since it forms no part of my invention, and is not .required for anunderstanding thereof Normally, ,thejdirectional relay DR, is released closing back contact 3 to connect the BSGil -l\l30.0 current source to the receiving apparatus the receiving apparatus is; normally conditioned forreception. With releyDR released to open.

frontcontactgtlie tubes i and 5 .oithepower amplierEA are without plate voltage and the transmitting, apparatus is nc-rmally-ginacti When fa pusl1 button PB l is operated to; close a Contact) a simple circuit` orenergizing relay DR. by current from a source whose terminals aredesf, ignated Band C is completed and relay Dlts picked 4to sw it cl^ i ,the B30 0 -N3Q0 current source` from the; receiving apparatus tol tubes li and 5 of the pcwermarnplierwand the transmitting apparatus yis made activefor supplyingpomf.,

munication current, suclicurrent beingdeliyered.

toa secondarywinding liiof output transformer. Tl at a relatively high energy level.

This transmitting apparatus isalso operable to supply current of a preselected frequency withinthe preselectedside band for calling and. signaling purposes.. Such calling currentniaybe, created by shifting the 4frequency of tl1e oscilla. tor OS a predetermined voice f1equency a1'1das` here shown this is doneby disconnecting a condenser l l from the oscillating circuit of oscillator OS,1o-scillator OSbeingcf the electron tube type; A calling relay DRl is normally..releasedtoiclose. back contact rHand connect condenser litter-he oscillatingcircuit of oscillator-@Sand the oscillator is conditioned'todeliver a carrier freouency, as preselected or `telephone purposes. Operation of a push button FB2, completes at ,its conf. tact i3 a simple circuitV for energizingrelays DR, and DRlin series. The pick'ngup cfrelayDPti;

t0 @een beck @Riedl iisermeeis Condenserl I A source ot current; whose terminals are identified at B300 and N3 0O is connected to these plate circuits tlirougli a, front Contact 8 of a directional relay.DR -and a. Winding'of alrelay RF, both of whicnrelays wille Deir beine Shown ie 'the'. deewiee-f: This. Semin loopl circuitcan be ;trac ed frorn en;e terminalsof` uehcoriduter and the oscillator OS is conditioned to deliver a carrier current of a frequency equal to the original frequency plus a preselected voice frequency. Since relay DR is also picked up to apply plate voltage to the tubes of the power amplifier PA, the calling current is supplied to winding l; ol` output-transformer TI at/ a relatiyely high energylevel. Byv way of illustration, I shall assume that oscillator OS is normally conditioned to deliver a carrier current of 5700 cycles per second, voice frequencies-or the range of 400 to 250i) cyclesper 'secondaire used for modulation and the ur'per side band is selected by filter BPF. Thuswitii directional relay DR picked up lcall-ingurel'ayDlftreleased a carrier Uelephone "current of the irequency range of 6.? 00 to S200 cycles is supplied to winding lil of tne output transormer. Furthermore, I snail assume that the carrier current is raised 100G cycles to 6709 cycles per second when condenser li is disconnetted! Carrier, Current. @t SWG- Grd fbeieeihe eque/elett Y' 0f the; Ori deel- Carrier, .of

up calling current o 670,0 1cyc1es- CSiS FFODQfiiQned-PO eeiesfiuae the-circuit SL: forth? Gefrier telephone Curr-eat. and preferablyl the iruitSL iune -1 to. resonane .atsomemid freetime! 0i the @er 'eri-telephone Currentand;

alfe mail? 0f eletlvely: i 1ere@ gCMS.s: Sefftiori so thatlthe resistanceof theK circuit Iis -relatively 10i?? eed' its? @retellimeedeesefis saches; to 'place substantially `full4 loaden the transmitting apf According to my in vention, circuitSL has as.- sociated ytl'ierevvi'th'` low power factor'inductancet Larload reac,tance LP, and relay Inductance L isconnectedacross,conductors flo and I8.'

1 overloacl;` contactl I9 kof relay RE', and loadfref..

actance: LP is connected acrossswinding I0 ofl transformer. TI over, back contactil of relay RF., Inductance L may be, for example, anv'air core coil, and load reactance LB maybe',,for example,

C. an yiron core'coil.

- In descfibieeihe Operation of the apparatus: of Fig.- 1,1 snallvasisume that, cabcoseV CO is not movingand that the contactjbetween atleast one pair of the Wheelsand thetracl;railswis'of a relatively high resistance due to some abnor-Y mal-condition on tliersurface of the rails. The normal. procedure in` initiating ycom munication in a train communication Vsystem is'ior an' op erator torst transmit calling current to inform thel operator yat V-tlie associated remote station that..telephonecommunication is desired, and- Ato this end tl'ie operatorat the caboose CO actuates push-button Pea mpick up. both relays Daa'nd DRI to condition the transmitting apparatus for supplying thecallingcurrent.. VWhen plate volt-- er Sewndfie supplied to the winding lil of output transformer.

n Thi Tne .sendingylooo circuit. Slinconnects; winding,v i 0 of transiormer: T l v.to the two. pairs. of-vwneels l -age is applied to tubes 4 and 5 of the power amplifier, the relay RF is also energized, but relay RF is provided with a predetermined slow pick-up period, and hence there is an interval during which relay RF remains released, after relays DR and DRI are picked up; During this slow pick-up period of relay RF, there are two circuit paths acrosslsecondary winding l0, one path including condenser CS, lback contact I9 of relay RF and inductance LI, and the other path including load reactance'LP and back contact Yof .relay RF.l The temporary circuit formed by load reactance LP in multiplewith condenser CS and inductance L in series is proportioned for parallel resonance at the frequency of the calling current, and thus the current owing through condenser CS and inductance L is large as compared to the output current of transformer Ti with the result a high voltage yis created across inductance L. This voltage created across inductance L is applied to conductors I Ei and i3 and hence is available for breaking down the resistance of the assumed high resistance contact between wheels I 4 'and the rails. If the .resistance of the wheel-to-rail contact is going to break down at allit `will nearly always do so immediately and also when such resistance is once broken down it remains at its usualflow value. Thus, the high voltage developed across inductance VL during the slow `pick-up period of relay RF is usually suiicient forbreakingdown any high resistance ata wheel-to-rail contact.

By way of example, a sending loop circuit 'of the type here involved may have a normal re' sist-ance of the order of 0.10 ohm and a power factor of about i0 per cent, giving acircuit impedance of about 1.0 ohm. The transmitting'apparatus may have a full load `output of 100 watts which would make a normal load `current Yof about S2 amperes for the sendingloop circuit. The temporary circuit formed by inductance L and load Vreactance LP should consume `100 watts, the full load of the transmitting appa-- ratus. Inductance L may have a power factor of 2 per cent, a practical value-for an air core coil, and a resistanceV of about 0.021ohm. Condenser CSmay have ail percent power factor and an apparent resistance 'of about 0.01 ohm. Thisgives a tctalresistance of 0.03 for'the two devices L and CS in series. Consideringthat the power loss through inductance' L and condenser CS- to be 90 watts, the current owing Vtherethrougl'i would be 55 amperes'4 For the transmitting apparatus to deliver .its

temporary circuit its output.

sumed in the temporary circuit 100 watts, which l is the full output of the transmitting apparatus. Underthese conditions inductance L would have a reactance of about 0.95 ohm giving a voltage across its terminals ofabout 52 volts (0.95 X55), and which 52 volts are available for breaking down the resistance of the wheel-to-rail contact. y

When only directional relay DR is picked up to vinitiate telephone communication, the telephone current creates no appreciable breakdown voltage during the pick-up period of relay RF. It is clear that in Fig. 1 a condenser may be used for the reactance LP in place of an inductor and the apparatus will operate in substantially the same manner as described above.

In Fig. 2, a vehicle CO of a railway train is provided with communication lapparatus including transmitting apparatus of a construction similar vto that of Fig. l, except a parallel condenser CP replaces series condenser CS and a series'load reactance LS replaces parallel reactance LP. `Also relay RF of Fig. 1 is replaced by a relay RFI and the switching means is modied to condition circuit SL to develop a breakdown voltageY whenever the transmitting apparatus is being conditioned for supplying a telephone current as well as when it is being conditioned for supplying a 'calling current.

Looking at Fig. 2, operati-on of push button FB2 for sending calling current completes a circuit for energizing relays RFI DR and DRI in series, such circuit Vextending from terminal B through the windings of relays RFE, DR and DRI in series, and contact iof push button FB2 to tothe picking up of relay 'RFL terminal C. Relay RFI is provided with a slow pick-up period and consequently relay DR is picked upto connect the BSO-NOG current source to the tubes and 5 of the power ampliiier PA and relay DRi is picked up to condition oscillator OS to supply the callingv current prior With relay RFI released, the low power factor inducta'nce L is connected across conductors it and I over back Contact 2l of relay RFI and load reactance LS is connected across winding i3 in series with inductance L andcondenser CP in parallel. The susceptance of indu-stance L is made slightly less :than that of condenser CP and load reactance LS tunes out the resulting capacitance reactance of condenser CPY and inductance L in parallel so 1 that'transformer TiV feeds the calling current into aY temporary circuit having a resistance that places substantially iull load Von the transmitting apparatus. Hence a relatively high voltage vis developed across inductance L in the manner described in connection with'Fig. l, and which volt'- age is available for breaking down the resistance -of the wheel-to-rail contacts. At the end of the Y slow pick-up period of relay RFI, the relay picks up to disconnect inductance L at back contact I 9 and to short circuit load reactance LS at front contact 22 and the sending loop circuit 'SL is then in its normal condition for transmission of the calling current. I'nthe event push button PBI is operated to condition the transmitting apparatus for supplying carrier telephone current, a circuit is rst formed from terminal B through windings of relaysRF-I, DR and DRI, back contact 23, and transfer contact 24 of a continuity transfer Contact for relay RFE, and Contact 9 of push button PBi to terminal C, and the three relays are energized in series Ywii'zh relays DR and DRI being picked up immediately and relay RFI being picked up at the end of its slow pick-up period. Hence a calling current is iirst delivered to the temporary circuit to develop a high voltage across conductors I5 and i8 for breaking down the resistance of the wheel-to-rail contacts. With relay RFI picked up, the relays RFI and DR are `held energized zover f-a :circuit .which passes: from terminal B through the windings of relays-'RFI fand ADR,i front co'rltact 2 5 'and 'transfer contact 24 offrelaylRFI Zand contact Sioipush' buttonPB I' .to

terminal yC.l Relay/DRI is .now-de nere-izedrand released; and-'oscillator IOS' conditioned tofsupply #the-original carrier current `usedFiortel'epl'ione `purposes. ,-With relay 'RF I pickedl up? the circuit fSL is switched 'to 'its norm-al condition fas explained above. It is to be: pointed' outv that' induetor-LS forthe-ioa'd reacta'iicevof Fig/2 maylbe Teplaced-by a condenser if'desired.

'11n Fig. .3,fa Caboose CO isV providedwtn transmitting apparatus sin-'lilarA totlaatf of Fig. 11;. except to `-include a serieel-parallel'- tunedf sending f. loop cifcuit andf al switching means ythat isfmo'died -toapplyfa'high break-downvoltage automaticaliy wheneverneeded insteadof being applied only avhen oneor the otherof the..l1:1us'h` :buttons-BBI aridPBZ is operated toinitiate either tireV` sending-'of -ca-llingror telephone current. ."Suchiswitching: '-means includes 1a 1 polar relayy RP, a neutral relay RF'Z and two rectifers Zfan'd-?. 'fRelay -RPI is preferably a twoWinding ybiased polar'relay,

contact members Sil-and 3 Iv oi'reiayRP are biased fw `to the ris-htas viewed fin=fFig. Sand the energiza- 'tioxr-foffwinding l2) Icy currentiowingin the-fdi- 'rection indioated'by the arrow; placed on winding ESE-energizes the relay to aid the bias toi position Athepolarcontactmembers S-'aind'si to theiright I vvto engagc'respective nornialpolar contacts. :iEnergiaation of Winding Z3 byfcurrent of thef'd- .rection lindicated by the arrow-placed on Winding .28'Jenergizes the relay to positionfcontactfmemf tiers Bwand Si to the ieft'toengage respective reverse polar contacts. Winding 29 is supplied Wit-h unidirectional current fromvv airansforiner T2 and rectiiier 2l, trans-Zorrner=T2l havingapri- Y,

Circuit -sL of rig. -3 '.normaiiy extends inem i' .top i terminarof f winding vI 0f cf .transormer' LTI throughserics condenservCS, backfconta'cti 35' of relay RFZp Winding-2 33'- of` transformer "112.V` con- -d'uctorfi8, wheels15; track rails-'Wheels'A Mfand yconductor l I6x -to ythe lower-terminal. of= -Win'dnfig 40. A condenserCP isS-comrectediacross thecirlcuit and the two ycondensers CSV and CP seryeito series-parallel -tune the circuity for the'v 'communication-- current. 'Such `aseries-paralleltuned circuitSL'supplies-current'to 'the rails' off-a'value equalvto` that supplied l by either the' 'series 'tuned -circuitoffA Fig.' lwor the parallel tuned circuitf'of Fi-g: 2 -yfor a given-fullli'oad condition of the trans- -mittingl apparatus gives `a little-higher 'Xml'tage facrossthe' `Wheel-tc--railV Contact andv permits' a very much simpler construction fc-r fthe' output transformer TI because its vsecondary currentflil Fcan be relatively small.

to close contact- -I3--toV *energize* relays ER land DRI* -inseries and `condition -the-transmitting apparatus -for supplying calling'current, `the energizationof WindingA -28 bycu-rrent supplied `:from

windingV -I of transformer T! lthrough?'rectifier Nfsinsicient totovercome the energizatinntof minding '29 lby the :current supplied ffrom transformer'fIZ '.'tlnough recti'er' I 'iff no high resistance ',wheel-to-railconta'ct exists. .Reiay f-RPis thus. heldat: itsrnormal right-"banda positionzwvith vthe result'thatzcircuitfSLiis retained nlitsinormal condition for. 'supplying the callinacurrent'to the rails. iAssumingi mow .thatra `high.resistance wheehtcerailccnta'ct develepsfat eitherfwfxeeis. ori, merg-ization of'winding291isrdecr'easd and iszovercome `:by Tthe i energization 'cf "winding 118, 'and relay-'RF1 is 'operated to its left-hand position toclose reversezpolar contacten fand causefV relay RF-2 itoibepicked up. iThezpickingnpnfzrelaY BF2 'tocperr .backcontactf 3 5=1and`c1oset front :contact :36 removes they short .,circuitifromfloadrreactance :13S :and 'connectsr-.low .power: factor inductance .Lacrosscccnductors lifean'df t8, winding '33 of-transformer Trbeingin thevconn'ectioni-to conductory I8. IIIductance :L andrreactamcezLS havefsuchwalluesi that the temporary fcircnit .they `form fwithf condensers CSuandCP :places: ci: fll load condition on. the transmittingapparatusan'd develops'fa 1 high "vcltagef across inductance .L in substantially Vthe .same manner :as @explained in Fig. 1, ainda-this: :big-h fvoltagexis applied* toscanductors fIlSf-and I8 forV bieaking'down:theifresistancexof .the- Wheelttoerail'V contact. lWVhen such high resistance #breaksy Aclown :current'zagain 'flows in winding- 33or transformer T2'. and winding. isnreenergizedf causingr relay *IR-P'V to. be 'operated toits normal. right-hand positioncwith the 'result tliatftlfiev sending'floop:A circuit vLISis-'switched to its normal condition.

-I-nthe event; lpush button: PBI is' operatedfto energize relayDR and condition' the transmitting apparatus-to -supply carrier telephone zcurrent, this cai-ren telephone current iis-f supplied; tothe sendingy loopv circuit-SL- iin: itsfnormal; condition.

Itfisqto bei jpointedf out that relay. BR :of Eigj is energized =by-a :circuit whichgpassesffrom termi-nallB through-Winding of --relayy DR,: normal polar contact 3'I\ of relay. RP 4Aand rcontactuscof .push Jbutton, BB It. -toaV terminal C. x 'AssumingA .that

.during-the transmissionA yof telephone-:currentea high Wheel-to-rail contactY resistance ldevelops, .then relay Epis-operated to its fleft-handpcsition. to pick l,up relay -Rzand switch .the 4sending circuitz-SLfto the temporary circuit conditionall- 'clliding :.inductance ,L `and load "reactance LS. Also awcircuit isafnow-formed-'from' terminal'iB through-windingsof relays DR and DRLinsees, 'reverse polar.. contact s BI-t 'fof 'relayf R'Pyiad contact 9 of push button PBI to. terminal C, and both relays DRI 'andi DRfiare -energized so that the transmitting apparatus is conditioned to sup- .'ply calling -cumentlwith thehresult'thatfa high 1voltagewis :developed :across inductance YL-for ibreaking' dou/nav the resistance-ofi tlie-wheeli-to- Y. .rait-contact. --f-Vilhen:the highfxre'sistance of the wheeltof'-rail'l contactrioreaks idownj -then IArela-y RP .is-restoredy to its normal fp'ositiondeenergiz- Aing frelayr- RF2 "fand: reestablishing the normal conditionsof-ncircuitfSL. TDRI Lis-now `deenereized and'releasednso ithat. the v`cscilflator deliversthe. original carrier nurrenti used for telefphone purposes. '.iltfis toi'Y beiscenftherefo-re th'at ftheaapparatuswof: Fig; 3=. automatically switches the. circuit SL :to a 'condition for developing= a. high-:breakdown voltage andcondtions the'transmitting: apparatus :forrsupplyingcalling cur-rent Iwheneverl ai high- -Wheel-'to-rrait `:Contact occurs.

l. .Although iL have: 4herein lsh'own and desci'ibcd only.y three :forms foffiinfansmittingi `apparatusfor fraiiwayitrain communication systems' :embodying myV invention, it is to beunderstood that various changes and modifications may be made therein Ywithin the scope of :fthe appended claims without departingfrorn the spirit and scope of my invention.

Having thus described claimis: i, Y

1. In train carried transmitting "apparatus for a railway train communication system using a sendingloop circuit interposed between the transmitting apparatusand two spaced wheels of the train to supply communication current to the rails, the combination comprising, an inductance, a load reactance, and switching means operablev at times to connect said inductance and load reactance'to said sending'loop circuit to develop a voltage for breaking down the resistance of'a wheel-to-rail contact of said sending circuit.

21.'In train carried transmitting apparatus for a railway train communicationsystemV using a sending loop circuit interposed between the transmitting apparatus and two spaced wheels 'of the train to supply communication current to the rails, the combinationv comprising, a lowpower factor inductance; 'a load reactance, a relay, circuit means including a contact of said relay to connect said inductance and-load reactance to said sending loop circuit to develop a voltage `to reak down the resistance of a wheel-to-rail contact of said sending said relay. Y

3. In train carried transmitting apparatus for a railway train communication system using a sending loop circuit interposed between the trans- Y my inyention; lwhat I miti-,ing apparatus and twospaced pairs of wheels of the train to supply communication current to the rails,"the combination comprising, condenser means connected to the sendingv loop circuit to tune the circuit to resonance at agiven frequency, an inductance, Ia load reactance, "circuit means including a contact to electrically associate said inductance and load reactance with said condenser means to develop a high voltagg in said sending loop circuit to break down the resistance or the wheeltorail contact at either of said spaced pairs of wheels when current of said given frequency is supplied by the transmitting apparatus, and means to control the contact of said circuit means and to condition the transmitting apn paratus to supply current of said given frequency.

e. In train carried transmitting apparatus for a railway train"communication'system using a sending loop circuit interposed'between the transmitting apparatus and two spaced pairs of wheels oi the train to supply communicatioh'current rto the rails, the combination comprising, reactance means connected to said sending loop circuit to tune the circuit to resonance at a preselected frequency,` an inductanceja'load reactance, and slow acting switching meas operable to simultaneously Yand temporarily connect said indu-stance and load reactance to said sending loop'ci cuit and to condition the transmitting 'apparatus to supply current ci said preselected frequency for developing a high'voltageacrcssthe wheelto-rail contacts ci said sending loopcircuit to break down the resistance of such wnee1-to-rail contacts.

5. In train carried transmitting apparatus for railway train communica on system, the com# bination comprising, a sen ng loop circuit including a winding coupled `to the transmitting apparatus and two conductors connected one to each of two spaced pairs of wheels-of the train to cause communication current supplied by the transmitting apparatus to flow through the rails becircuit, and means tocontrol tween suchspaced wheels, an inductance, a load reactance, and switching means including circuit controllingcontacts to connect said inductance and load reactance to said conductors to form across said winding a temporary circuit independent of said wheels and rails to create a voltage across said conductors for ,breaking down the resistancevof a wheel-to-rail contact. 1 1

`6. In train carried transmitting apparatuslv for a railway train communication system, the com'- bination comprising, a sending loop circuit inter,- posed between the transmitting apparatus. and two. spaced pairs of wheels of the train to-include a given length of the rails in such loop circuit, capacitance means interposed in the sending loop circuit to tune the circuit to resonance at a given frequency, said ksending loop circuit formed to provide a circuit impedance that places a full load on said transmitting apparatus, reactance means, and switching means to at times connect said reactance means to said sending loop circuit to'restore said iull load condition and simultaneously develop a high voltage when there is a high resistance wheel-to-rail Contact in said sending circuit, l

7. In train carried transmitting apparatus for a railway train communication system, the com; bination comprising, a sending loop 'circuit including a winding coupled to the transmitting apparatus and conductors connected to spaced pairs of wheels of the train to cause vcommunication current supplied by the transmitting apparatus to flow through the rails between such spaced vpairs of wheels, said loop circuit tuned and lformed for an impedance which places a substantially full load on the transmitting apparatus, an inductance, a load reactance, switching means including circuit controlling contactsl toY connect said inductance and load reactance to said winding to form a temporary circuit in multiple with the path of the loop circuit throughsaid wheels and `track rails and which temporary circuit has a tuning and impedance substantially equal to that of said loop circuitV to develop aK voltage across thev loop circuit path through the wheels and rails for breaking downthe resistance'at a wheel-to-rail Contact of-'the `loop circuit, vand means to control said switching'rneans.

8. In train carried transmitting apparatus for a railway train communicationV system, the combination comprising, two conductors to connect the output terminals of the transmitting apparatus to two spaced pairs of wheelsfof thetrain to form a sending loop circuit including a given length of track rails, condenser means connected to said'rconductors to tune said sending loop circuit, Van inductance, a reactance, a relay, circuit means including contacts of said relay to connect said rinductance and reactance to said condenser means to formacross the output terminals/of the transmitting apparatus a temporary circuit'hav ing an impedance and tuning substantially equal to those of said loop circuit for applying a high voltage across said conductors of said loop cir-'-` cuit when current of said given frequency is sup plied by the transmitting apparatus; and man# ually operable'means to control said relay and to condition the transmitting apparatus'to supply current of saidV given frequency.

9.' Inftrain carried transmitting apparatus for railway trainv communication systems, the comi bination comprising, a sending loop circuitin'- cluding arwinding coupled to said transmitting apparatus and two conductors connected one to each of two spaced pairs of wheels of the train the rails between-said spaced. Wheels, a .condenser connected tok said: loop l.circuit :to vtune :said: loop circuit fto'resonance at a giyenfrequency, anxinductancaareactance a relay, vcircuit meansincluding: a :contactof 'said-:relay tozconnectzsaid inductance :and `reactancetot saidrwinding. to` form a temporary circuit ihavngv. an impedance; sub'- stantial-ly equal .to that of saidslcop .circuit 'to` receive :current from l the transmitting; apparatus to: create. across r said. conductors sa 'high 4Voltage for: breaking 4downl .the :wheel-.lto-rail. contact resistancevof the fsendingdoop circuit; andimeans tez-control saidrelay and torconditon'said trans; mitting .apparatus tov supplyv cur-.rent 10i said 'given frequency.

l; .Inf train carriedftransrnittingirapparatus fior supplying .seither a carrier telephone current 'or.1a callingV current. having a preselectedffrequency ot'thete1ephone current; Athey combination .come pulsing; asendingi-loop :circuit includingawinding coupled.: to the transmitting: apparatus r and two conductors connect-cd1. fone to ieachiof iftwo. Ispaced pairs `of wheelszof the-train toca-use current. from the transmitting apparatus to ilo-w in thefrails betweenzsucltil spacedrpairs of ;.wl1eels,.- an inductance, aiload1reactance ,f-.switchingfmeans including circuit :icontrollingifcontacts :to connect said inductance and loadureactan-ce to ,said winding to form la.: .temporary circuit in multiple with .the

wheels" :and-tirails'cf the sending-loop,circuit and saidrtemporary-fcircuit tunedtoirescnance at the frequencyfcf the 4'calling current tof develop.y a voltage acrosssaid conductors -:for breaking- .down tliez'resistanceoafwheeleto-rail .contact of the sending. .i loop; circuit, andy manually operable meansv to control said-switching, meansfand. to condition;v lthe Atransmitting apparatus to supply callingzcurrent-- l1. .In'train icarreditransmitting .apparatus for supplying-;..eitlienav carrier telephone current or a callingpcurrent .hai-fing preselected )frequency of the 1telephonefcurrent, the `combination --ccafnprising, sendingaloop: circuiti including` Ya winding -coupledito the"transmittngrspparatus =and two conductorsaconnected oneztofeachvv ofotwo spaced pairs-ofwheels fof the train, Yaircondenserinterposed in one fof-.said conductors toeseries'tunethe loop:.circuit forsaid;telephone:currentsan inductan'ce', ailoa'dgreacta-n'ce; aslowfpick-up" relay providcd'nvith baclcLcontacts-to connect :saidz'inductangeflacrcss. saidy conductors and toy :connect sa-id load: reactancearacross said winding toforn'rxwith saldicondenser :a :temporary circuit series-parallel tunedstoresonancev at said preselectedircqucncy,

and manually voperable'"ineens towcondition the transmitting apparatus lto suppiyfcallinggcurrent andtorenerigizo said relayto develop; bysaid ternnotary?'circuity during the slow pick-up, period of said: relay :al voltage; across; .said conductorsY to breakdovm the 5 resist-ance of l' the wheelPto-rail contact Lat saidV wheels. Y 12. `In' :train carried'transmittingeapparatus ier slmplyng either; afcarrieptelephone current -or a calling current having a preseleotedfrequency of the'teiephonefcurrcnt. tbe-combination comprising; ascending ioopcir `iit including. a'windjng coupled i to 'tice transmitting@ apparatus :and two conductors connected one--to each; .ofitwo spaced PrSfof'- wheelsct: the.Y train; cm2-condenser" connected acrossseid conductorsrto parallel tunefthe loopL circuit-to low virnpedance-forI said. telephone current; .an inductance; ay .reactance element inf terposedin one ci saidzconductors, a slow. pick-up relay provided with aback. contactto connect saidinductance acrosssaid conductors and. a front contact to short circuit said'reactance element to form with said condenser a special :cincuit across said winding, said. special circuitzof low impedance and'tuned to resonance at said preselected freduency'to develop avoltage across saidinductance ioribreakingdow-n the resistance of 'a-wheelsto-rail contact :at saidspacedi wheels, and. manually operable `meansfzto 'simultaneously condition the transmittingapparatus l' to supply calling vcurrent and-.toenergize said slow pick-.up relay..

13.` In train .carried 'transmitting apparatus for supplying a carrier telephone current, the com'- binationcomprising, asending loop circuitin cludingtwoeconductors connected one between one'routput terminal of thel transmitting apparatus and a .first-pair ofwheels of the train and Vthe other conductor conncctedbetween thepther output terminal of the transmittingy apparatus and Ia second.' pair loi `Wheels of the train, aflrst reactance element interposed in series :in saidk one conducto-r, and -a second reactance element connected across said two: conductorspto cooperate with said first reactance element to series-petals lel tune said sending loop `circuit for said carrier telephone current.

14. In train carried :transmitting apparatus for supplying a carrier telephone current the combinaton comprising, awinding coupled to said tranemittingv apparatusto-receive such telephone current, two conductors connected one between oner terminal of said winding. and a first pair'of wheels of the train andthe other between the other terminal- .of said winding: and a second-pair of wheels of thetrainto form asending `loop circuit completed through the rails between said rst and lsecond pairsoi wheels; a rstlcondenser interposed in said'oneconductor, and a second con- `denserconnected across said two conductors to cooperate with said ,rst `.condenser .to series-parallel tune said lloop circuit to low impedance -ior said telephone current;

15. YInni-,rain carried transmitting apparatus for supplying either a carrier telephone current or a calling `current having. a preselected frequency of such telephone current, the. combination compris-v ing, a iirst transformer-having a rst winding connected to. said transmitting apparatus to receive said telephone andcalling currents, a'second transformer; a sending-loop circuit including enseccndv Winding of said rst transformer, a rst winding. of Vsaid secondtransformer, two conductors connected one toeach of the two spaced pairs of the wheels o the train .and they rails between said spaced pairs of wheels; aninductance, a load reactance, arelay jointly/,energized by energy rcceived from the second winding of said irst transformer and from a 'second Winding'of'said second transformer, circuit means controlled by said relay toconnect said inductance and said Yload -reactance to said sending loop circuit to develop a voltage for breaking down the resistance of a wheel-to-rail Contact of eitherone of saidpairs of wheels when said calling current is supplied by the transmitting apparatus, and other circuit means controlled by said relay to condition the traismitting apparatus to supply-said callingvcurren AUSTIN M, yCRAVA'IH. 

